Conventionally, a wind turbine may be operated using a fixed or constant target rotational speed (also referred to as reference rotational speed or rotational speed set-point) and a fixed target power (also referred to as a reference power or a power set-point). In these conventional systems, a turbine controller may aim to hold this fixed target rotational speed and fixed target power at high wind speeds. In this case, there should be a sufficiently high wind speed in order to operate at these targets, otherwise the speed and/or power may be lower. The maximum rotational speed and the maximum power, where the mechanical structure or the electrical components will be damaged may lie above the target rotational speed and the target power.
Document EP 2 128 437 A2 discloses a method for increasing energy capture in a wind turbine, wherein an adjusted rotational speed set-point greater than the initial rotational speed set-point is determined in response to operational parameters which may include standardized environmental conditions, such as average wind speed, turbulence intensity or air density and the operational parameters may include generator speed, power output, turbulence intensity, wind shear, combination of ambient temperature and air pressure, air density, component temperatures, generator torque, current and generator rotor and stator, voltage in generator rotor and stator, power factor, power top vibration, drive train vibrations, yaw position and combinations thereof.
It has been observed that conventional wind turbines and wind turbine controllers and control methods are not in every situation capable of operating the wind turbine such as to provide satisfactory power production.
A technical problem to be solved by the present invention may be regarded as providing a method and an arrangement for controlling a wind turbine, wherein energy output of the wind turbine may be improved, while maintaining a secure operation and while avoiding damage or excessive loads on components of the wind turbine.